ASSESSMENT OF CLIMATE AND LANDUSE CHANGE IMPACTS ON WATER BALANCE

Abstract

Occurrences of climate change are globally recognized and is responsible for various significant impacts on the hydrological cycle, which influences the rainfall and evapotranspiration. Increasing temperature is also affecting the environment leading to global warming and these changes may cause adverse impact on the economy, agriculture, fresh water supply and water resources availability. Human intervention is also responsible for various environmental changes and in the future, these may lead to shortages of food and water supply. However, appropriate measures, proper evaluation of the situation and awareness among people may help in successful management. In this study, climate trend analysis is done with the historical data and future prediction of climate is carried out to understand the climate condition of the study area. Landuse change analysis is carried out, which shows the human impact on the landscape and estimation of future landuse change is done to observe and assess the change effects of climate and landuse on the water balance of the study area at present and in the future. Spatial actual evapotranspiration (ET) is estimated from the energy balance method to see the effect of ET on water balance and comparison of actual ET estimated from energy balance and from the water balance equation have been compared to obtain the model that gives a better estimation of water yield for the study area. The trend analysis is carried out with rainfall, temperature and evapotranspiration with more than 100 years data for the entire state of Madhya Pradesh (MP) of India and for the basin study area in Madhya Pradesh, which is a part of the Narmada river basin. The rainfall trend for entire MP shows a decreasing trend annually and particularly in the monsoon time. Monsoon season is the major contributor of rainfall in a year and decrease in monsoon rainfall is reflected in the reduced total annual rainfall of MP. The annual decrease of -6.75% of rainfall is observed from 1901 to 2011. Minimum, maximum and mean temperatures of MP have shown a significant increase in almost all the seasons and also in the annual series. The evapotranspiration trend also indicates an increase in most of the stations of MP and in almost all the seasons. The trends of temperatures and ET show a similar distribution pattern of increase and decrease. The rainfall trend analysis is carried out for 111 years from 1901 to 2011 and the temperatures and ET trends have been done for 105 years from 1901 to 2005. Analysis of net increase or decrease in overall rainfall, temperatures and ET in MP is performed to ii assess the effect of climate of the area. The results show a net deficit in the rainfall amount and the net gain in the temperature and ET0 amount. Future rainfall, temperature and evapotranspiration are generated using the General Circulation Model (GCM) data and by the Least-Square Support Vector Machine (LS-SVM) and Statistical DownScaling Model (SDSM) models. Future projection of climate data is done for three stations of the study area viz., Betul, Hoshangabad and Raisen. The rainfall, minimum and maximum temperature show increase in future in both the models. Future ET also shows an increase by both LS-SVM and SDSM, but there are some fluctuations with decrease between the decades. The Maximum Likelihood Classification (MLC) is used for the landuse classification of 1990, 2000 and 2011 and Markov Chain Model has been used to project future landuse change of 2020 and 2050. The future projection of landuse change indicated the conversion of forest and other vegetation to the agricultural lands and settlements. Wastelands are also observed to have converted to agricultural lands in this area in the future. The study area is mainly agricultural, and there is constant encroachment of the settlements and agricultural lands within the vegetation and wasteland areas. Some stony surfaces are also observed along with some areas of the river and lakes. A highest decrease of forest area is projected in 2050, while 1990 shows highest forest cover. There is also an interchange of areas among forest, open forest and grasslands. The spatial actual ET is generated from the Surface Energy Balance Algorithm for Land (SEBAL) for the study area on monthly, seasonal and annual basis of 2011. The spatial actual ET shows close resemblance in pattern with the Normalized Difference Vegetation Index (NDVI) in different time of the year. The ET also shows variation with respect to different landuse, which indicates an increase over the forest and vegetated area and over full mature crop lands. But it decreases after crop harvesting. The ET is low in the monsoon season because of high humidity in the air, and is very high in the pre-monsoon or summer season. The overall annual ET shows higher ET over forest areas than in other parts. The future landuse impact on future ET is also calculated that shows a gradual decrease in the actual ET because of the constant removal of the forest areas, which is projected to be maximum in 2050. The impact of climate and landuse changes on water balance of the study areas is assessed and future prediction is given by the Soil and Water Assessment Tool (SWAT) model. The climate change impact results in increased total water yield and evapotranspiration. The landuse change impact shows increased water yield, but decreased ET, while combined effects of climate and landuse change depict increased water yield and surface runoff but reduced ET in the future. Therefore, the impact of climate is found to be pronounced on water yield, while impact of landuse change is dominant over ET. The total water yield estimated by SWAT is 401.28 mm against the observed data of iii 291.11 mm in 2011. However, the water yield obtained from SEBAL model by generating spatial ET gives 317.87 mm in 2011, which is closer to the observed value. Hence, the compared results show better accuracy of the SEBAL model in estimating water balance of the study area than the SWAT model, although the future projection of water yield is calculated by SWAT only in this case. The overall results indicate increased surface runoff and water yield and decreased actual ET in future due to climate and landuse changes. Nevertheless, existence of uncertainty in the model outputs could not be ignored and there are also complex relations within the interactions of climate, landuse and hydrological cycle, and to come to any deduction is quite difficult. However, studies regarding the changing climate and landuse, how it is affecting the environment and natural resources can be assessed to give some evaluation of the immediate problems that need attention. The study shows the effect that is exerted by reduced vegetation and changing climate and also the effect of changing ET by energy balance, which is influencing the water balance of the area, and proper management processes might be helpful in the future.